Nature versus nurture is dead – long live epigenetics!

Darwin and Freud walk into a bar. Two alcoholic mice — a mother and her son — sit on two bar stools, lapping gin from two thimbles.

The mother mouse looks up and says, “Hey, geniuses, tell me how my son got into this sorry state.”

“Bad inheritance,” says Darwin.

“Bad mothering,” says Freud.

_______

The nature / nurture debate has divided scientists and philosophers for millennia. Plato and Aristotle, as they generally did, had opposing views on the subject. John Locke, the famous 17th-century philosopher posited that the human mind is a tabula rasa (blank slate) upon which the environment inscribes personality. This view has generally held sway in the social sciences. But its opponents believe that it is genes which control our behaviour. This has been a very polarising debate. One man who experienced all this divisiveness was E.O. Wilson. A proponent of sociobiology, Wilson was accused of racism, misogyny, and eugenics. At a two-day symposium organised by American Association for the Advancement of Science, he was attacked by a member the International Committee Against Racism, who poured a pitcher of ice water on his head and chanted “Wilson, you’re all wet.” The scientist, still wet, gave his speech and received a prolonged standing ovation. No one was asked to leave the premises, no police were called, and no action was taken against the protesters later. Such is the indulgence given to these intellectual fascists on campuses and at public meetings. Wilson, though, was proud to be the target of such intolerance:

“I believe…I was the only scientist in modern times to be physically attacked for an idea.”

I have tended to side with those on the side of genes, but really this debate is based on a false dichotomy. Genes and environment interact. The best explanation I have read about this was by Matt Ridley in his book Nature via Nurture, which came out in 2003:

It is genes that allow the human mind to learn, to remember, to imitate, to imprint, to absorb culture and to express instincts. Genes are not puppet masters, nor blueprints. Nor are they just the carriers of heredity. They are active during life; they switch each other on and off; they respond to the environment. They may direct the construction of the body and brain in the womb, but then they set about dismantling and rebuilding what they have made almost at once – in response to experience. They are both cause and consequence of our actions. Somehow the adherents of the ’nurture’ side of the argument have scared themselves silly at the power and inevitability of genes, and missed the greatest lesson of all: the genes are on their side.

In the light of this controversy I have been following with great interest the emerging field of epigenetics. Although it has been defined in several ways, all the definitions are based on the concept that environmental forces affect gene behaviour, either turning genes on or off. I found this definition online:

Epigenetics literally means “above” or “on top of” genetics. It refers to external modifications to DNA that turn genes “on” or “off.” These modifications do not change the DNA sequence, but instead, they affect how cells “read” genes.

Genes contain the instructions but it is epigenetic factors which direct how those instructions are actually carried out. I don’t really understand the processes involved, but I’ll give it a go. There are two basic mechanisms for epigenetic change. One involves molecules known as methyl groups that latch on to DNA to suppress and silence gene expression; the other involves molecules known as acetyl groups, which activate and enhance gene expression. If you want to know more, check out the video above.

This epigenetic influence is ongoing. Fifty-year-old twins show three times more epigenetic modifications than do three-year-old twins; and twins reared apart show more epigenetic alterations than those who grow up together. Epigenetic investigations are proving that neither genes nor the environment is destiny.

A brief digression: epigenetics does seem to have echoes of the ideas of the 18th century naturalist Jean Baptiste Lamarck. He was writing about evolution long before Darwin. Unfortunately he backed the wrong horse, or should I say giraffe? He believed that the giraffe ancestors had stretched their necks to get at the highest leaves in the trees. This caused their necks to become slightly longer, which trait was passed on to descendants. Generation after generation inherited slightly longer necks, and the result is what we see in giraffes today. Darwin’s Origin of Species, Gregor Mendel’s peas and the later discovery of DNA left the Frenchman’s ideas looking ridiculous. The field of epigenetics is not exactly a vindication of Lamarckian evolution, but there are at least parallels in the transmission mechanism.

What are the practical implications of epigenetics? One fruitful area has been research into famines. Studies of the effects of famines in Holland in the 1940s, in China in the 1950s and in the United States over a century ago show they affected the lifespan and obesity rates in subsequent generations. The Dutch famine took place in the German-occupied part of the Netherlands during the winter of 1944-1945, as World War II was drawing to a close. A German blockade cut off food, punishing the Dutch for not supporting the Nazi war effort. One famous victim was Audrey Hepburn who was growing up in Holland during the famine. She would go on to suffer from anaemia, respiratory illnesses, and edema as a result. The clinical depression that afflicted her later in life has also been attributed to malnutrition. This tragedy and its longer-term consequences was the subject of the Dutch Famine Birth Cohort Study, which found that the children of pregnant women exposed to famine were more susceptible to diabetes, obesity, cardiovascular disease and many other health problems. The women who were pregnant children during the famine had smaller children. That is to be expected. What was more surprising was that when these children grew up and had offspring of their own, these children were also smaller than average. This data suggests that the famine experienced by the mothers caused some kind of epigenetic changes that were passed down to the next generation. Hunger seemed to switch on genes that increased the accumulation of body fat in times of plenty, in order to improve survival chances in times of famine.

However this is not helpful in the modern world where cheap calories are more easily available than at any time in history. These epigenetic effects could lead us to a rather pessimistic conclusion. But this knowledge could also be used to find solutions. There are apparently already four drugs on the market which can switch genes on or off. And if you don’t want drugs, you may be interested to know that diet can also affect gene express themselves and exercise has been shown to switch off the FTO gene, a key driver of obesity.

In coming decades, scientists studying epigenetics may understand how environmental forces and genes interact to condition our health. Epigenetic systems are heritable, self-perpetuating, and reversible. I am convinced we will find cures for many human diseases and conditions, including some cancers. And it may unlock some of the mysteries of human personality. I wouldn’t go as far as saying that it will be rendered obsolete, but I think epigenetics will give us a much more nuanced perspective on the nature-versus-nurture debate.